||Echinopsis chamaecereus f. lutea is a yellow, ornamental cactus species, which belongs to the group of mutant, chlorophyll-deficient cacti. Their inability to synthesize chlorophyll makes these chlorophyll-deficient cacti survive only if they are grafted onto adequate stock which contains chlorophyll. Chlorophyll-deficient cacti are multiplied through “in vitro” cloning. With regard to the establishment of an “in vitro” culture of Echinopsis chamaecereus f. lutea, from the parent plant grown in the greenhouse, we sampled 1-cm explants, which were used as stem segments that were inoculated on an aseptic agarose medium with macroelements and Murashige-Skoog FeEDTA (1962), Heller microelements (1953), vitamins – pyridoxine HCl, thyamine HCl, and nicotinic acid (1 mg/l of each) – m-inositol and sucrose, without growth regulators. In the grow room, the tissue cultures were illuminated with light-emitting diodes (LEDs) of different colors (yellow, red, green, blue or white), with a light intensity of 1000 lx. The evolution (rhizogenesis, callogenesis, and caulogenesis) of the in vitro cultures was monitored for 90 days, tracking the differences in reactivity to the different wavelengths of LEDs illumination. Cultures exposed to white light emitted by fluorescent tubes served as the control sample. After 90 days, compared to the differentiation of the control sample exposed to white light from fluorescent tubes, the samples grown in the presence of green or blue LEDs demonstrated statistically significant increases in the growth of the stems; under red or green LEDs illumination, calusogenesis intensified, while under white or yellow LEDs illumination, the rate of development of the stems was not significantly different from the growth of the control samples. Rhizogenesis was not observed in any of the samples.
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